An optical modulator is typically configured such that an input optical fiber and an output optical fiber are connected to opposite sides of a package in a series connection. However, connecting an input optical fiber and an output optical fiber to opposite sides of an optical modulator increases the size of the overall optical modulator and undesirably increases an area to be occupied by the optical modulator.
Under the circumstances, some optical modulators may be configured such that an input optical fiber and an output optical fiber arranged in parallel are connected to one side of a package for reduction of an area to be occupied by the optical modulator.
In an optical modulator, to which an input optical fiber and an output optical fiber arranged in parallel are connected, direction of light travel is changed between a tip of the input optical fiber and a tip of the output optical fiber. As a technique related to such changing direction of light travel, for instance, a technique that uses a mirror and an optical modulation chip is proposed. This technique causes light emerging from the tip of the input optical fiber to be reflected by the mirror toward a side surface, which serves as an incident facet, of the optical modulation chip and performs optical modulation on the reflected light while causing the reflected light to propagate to one facet, which perpendicularly intersects the side surface, of the optical modulation chip using a bent portion of an optical waveguide on the optical modulation chip. A light beam resulting from the optical modulation is output from the one facet, which serves as an exit facet, of the optical modulation chip to the tip of the output optical fiber.
Patent Document 1: Japanese Laid-open Patent Publication No. 2014-164243
An electro-optic crystal, such as lithium niobate (LiNbO3), is applied to an optical modulator chip in some cases. It is known that, in an optical modulation chip to which an electro-optic crystal is applied, if an optical waveguide on the optical modulation chip has a bent portion having a small refractive index, light will leak from this bent portion due to the small difference in refractive index between the optical waveguide on the optical modulation chip and the electro-optic crystal. Specifically, when light reflected from a mirror is caused to propagate to one facet that perpendicularly intersects a side surface of the optical modulation chip using the bent portion of the optical waveguide on the optical modulation chip, changing direction of light travel causes a problem of increase in loss.